Here, we consider the roles played by sharks and other top predators on the ecological workings of coral reefs. However, a complementary goal is to maintain the ecosystem services of these taxa. One goal of management is motivated by simple existence value especially of culturally important or charismatic species. The management of coral reefs often includes a goal to support viable populations of large predators. As such, the study of predator effects on coral reefs is less of an investigation of the binary categorization of ‘vulnerable’ vs ‘invulnerable’ to predation, but instead is one of relative levels of risk. Even those fishes thought to be among the most dominant predators, for example large-bodied sharks and groupers, can fall victim to predation themselves. Consider the myriad somatic and behavioral adaptations of most coral reef fishes that are linked putatively with predator avoidance - cryptic coloration, aggregation or schooling, and morphological changes. In fact, predation remains a ubiquitous threat for reef fishes of all types and sizes. Īlthough the instantaneous probability of predation tends to decrease through the life of an individual fish, the threat is never gone. And, as with many marine taxa, the probability of predation per unit time among coral reef fishes is highest for the smallest individuals. For a fish living on a coral reef, among the most critical type of experience is the understanding of the landscape of shelter for diurnally active reef fish, an intensive competition for shelter dominates at dusk as each fish searches for a hole, crevice, or other reef space where the individual can survive the night. The instantaneous threat of predation for a surviving individual drops with time, associated with an increase in experience and in body size. For example, a review of studies suggests that over 50% of individual fish settling from a pelagic-associated larval stage to a reef-associated juvenile phase die within 2 days of arrival. For most species of reef fish, the threat of predation begins at the earliest life stages, as fish recruiting to the reef face an intensive ‘predation gauntlet’. Predation is a dominant force defining the structure and dynamics of coral reef fish assemblages. Studying the effects of predators on coral reefs remains a timely pursuit, and we argue that efforts to focus on the specifics of vulnerability to predation among potential prey and other context-specific dimensions of mortality hold promise to expand our knowledge. Relatedly, individual fishes that suffer from debilitating conditions, such as heavy parasite loads, appear to realize relatively stronger levels of prey release with reduced predator density. For example, territorial damselfish appear to realize reliable population expansion with the reduction in predator density, likely because their aggressive, defensive behavior makes them distinctly vulnerable to predation. We find that some groups of fishes are particularly vulnerable to the effects of predators and more able to capitalize demographically when predator density is reduced. While such studies search for evidence of prey release among broad groups or guilds of potential prey, a subset of studies have sought evidence of release at finer population levels. Evidence of prey release has been observed across some reefs, namely that potential prey increase in density when predator density is reduced. Gradients in predator density have been created by spatial patterning of fisheries management. Many innovative studies have capitalized on natural experimental conditions to explore predator effects on reefs. Despite the threat presented by top predators, data describing their realized effects on reef community structure and functioning are challenging to produce. Among the most charismatic group of reef predators are the top predatory fishes, including sharks and large-bodied bony fishes.
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